1. Field of the Invention
The present invention relates to a thermal protector used in various kinds of electric components and appliances for protecting the electric components and appliances from over heating and over current accidents due to heating and overcurrent under abnormal conditions.
2. Description of the Prior Art
A conventional thermal protector has the following structure: An electrode mount comprising a movable electrode and a stationary electrode which are fixed with a glass bead so as to oppose to each other is contained in a glass envelope. The glass envelope is pinch-sealed by melting an opening thereof located under the glass bead. After being exhausted and filled with gas, the glass envelope is hermetically sealed by tipping off the top thereof. Such a structure is described in Japanese Utility Model Publication No. 56-42912.
The thermal protector with the above-mentioned structure is provided on a heating unit of various kinds of electric components and appliances. When a temperature of the unit is raised or an excess current flows through the unit due to some abnormality or other, a snap-acting and thermo-sensitive element of the movable electrode is reversed in order to be removed from the stationary electrode, thereby as a protective function shutting the current to the electric components or appliances.
Recently, as the electric components and appliances are made compact, there has been a desire for developing a thermal protector with a small size and an excellent opening sensibility in a low current region.
However, in the above-mentioned conventional structure, the desired opening sensibility of a compact thermal protector in a low current region cannot be obtained even if a resistance wire of a nickel-chromium alloy is used as a lead wire of the stationary and the movable electrodes in the glass envelope.